July 7, 2010

Horseshoe crab tagging looks at survival after being bled for medical research

Survival of horseshoe crabs after being bled for medical research and then released back into coastal waters is the focus of a two-year tagging study by the S.C. Department of Natural Resources and funded by the S.C. Sea Grant Consortium. The tags are supplied by the U.S. Fish and Wildlife Service.
To date 1,600 crabs have been tagged and released, and the public is urged to report tagged crabs through the toll free number printed on the white button tag attached to the shell.

For years these primitive animals have been captured on state beaches and transported to medical research facilities where a portion of their unique blue blood is extracted and used to make Limulus Amoebocyte Lysate, which is widely used to test for bacterial endotoxin contamination in human intravenous drugs and medical devices.

"We hope that tag reports over several years will demonstrate if biomedical bleeding is having a detrimental effect on horseshoe crab populations," said Larry DeLancey, S.C. Department of Natural Resources (DNR) biologist, who added that these animals are thought to be increasing in the Southeast.

About 100,000 horseshoe crabs are captured annually by licensed fishermen and taken to research facilities. Long-term survival rates of the crabs released after being bled is not known.

Not actually crabs but more closely related to spiders, these harmless animals spawn on state beaches every spring and their eggs are a vital food source for migrating shorebirds, many species of which have declined in recent years.

A recently completed study of 100 bled and tagged horseshoe crabs held in a pond at DNR's Waddell Mariculture Center in Bluffton had a survival rate of almost 90 percent, DeLancey said, noting the survival rate of crabs released into the wild might be different.

A separate study is assessing the economic impact of the horseshoe crab fishery on local commercial fishermen. Horseshoe crabs are protected by South Carolina law and the crabs, as well as their shell, cannot be taken unless by permit.

South Carolina's natural resources are essential for economic development and contribute nearly $30 billion and 230,000 jobs to the state's economy. Find out why Life's Better Outdoors.